1. Field of the Invention
The present invention relates to a zoom lens system which is suitable for a projection apparatus for enlarging/projecting an image formed, for example, on a display member onto a screen, and a projection apparatus using the zoom lens system.
2. Related Background Art
Various projection optical systems for enlarging/projecting film images or projection original images from liquid crystal light bulbs onto screens and various projection apparatuses (projectors) using such optical systems have been proposed.
With the recent demands for an increase in the resolution of a projector and a reduction in size, there are increasing demands for a projection optical system which is used for the projector and has higher optical performance in terms of resolution and compactness.
Recently, as the demand for an increase in the resolution of a projection optical system has increased, proper correction of chromatic aberration, in particular, has been required. As a method of properly correcting chromatic aberration (magnification chromatic aberration, in particular), a method using a diffractive optical element for an optical system is available.
A technique of applying a diffractive optical element having a diffraction effect to a zoom lens is disclosed in Japanese Patent Application Laid-Open No. 2000-19400 (corresponding to U.S. Pat. No. 6,081,389).
According to Japanese Patent Application Laid-Open No. 2000-19400, a diffractive optical element is provided for a zoom lens constituted by five lens units as a whole. By optimizing the shape of this diffractive optical element, a projection optical system is obtained, which has little astigmatism and distortion aberration and has properly corrected magnification chromatic aberration in accordance with a high-resolution liquid crystal. The zoom lens proposed in this reference aims at correcting chromatic aberration (magnification chromatic aberration, in particular). However, there is no description about a reduction in the size of the projection optical system.
In general, in a color liquid crystal projector using a liquid crystal panel for an original image to be projected, it is especially important to properly correct chromatic aberration of various aberrations in the projection optical system (projection lens). If the chromatic aberration in the projection lens is not properly corrected, the color of a projection image blurs, affecting the image quality. In addition, recently, an important issue is how to realize a reduction in the size of the projection lens with a reduction in the size of the overall projector as well as how to realize high image quality.
It is an object of the present invention to provide a zoom lens system which properly corrects chromatic aberration while realizing a reduction in the size of the overall lens system, and has good optical performance throughout the entire zooming range and the entire screen.
In order to achieve the above object, according to an aspect of the present invention, there is provided a zoom lens system comprising, from a first conjugate point side (screen side) at a longer distance to a second conjugate point side (original image side) at a shorter distance, a first lens unit having a negative optical power, a second lens unit, a third lens unit, a fourth lens unit, a fifth lens unit, and a sixth lens unit, wherein a plurality of lens units of the first to sixth lens units move for zooming, and at least one lens unit of the first to sixth lens units has a diffractive optical element.